Carbonless copy systems and other copying systems employing a color precursor and a developer are well known in the art. These systems can comprise two sheets, a transfer or donor sheet which contains a colorless color-forming agent on one of its surfaces which is often contained in pressure rupturable microcapsules and a developer or receiver sheet, which is typically a substrate having a layer of a developer material coated onto its front surface which can react with the colorless color-forming agent to form a visible image. In practice, to produce an image, the two sheets are juxtaposed so that the colorless color-forming agent faces the developer material. Upon the application of pressure, such as a pen, pencil, typewriter, or other writing instrument, the microcapsules are ruptured which releases the colorless color-forming agent. The color-forming agent reacts with the developer material on the developer sheet to form a visible image.
Transfer pressure-sensitive systems as described above are only one type of imaging system employing a color precursor and a developer. Other types that are known in the art are self-contained systems in which the color precursor and the developer are carried together on the same support (e.g., in the same or separate layers). Another type of copy system which employs a color precursor and a developer is thermal recording systems in which the color precursor is activated through the application of heat. Light sensitive copy systems such as the CYCOLOR system described in U.S. Pat. No. 4,399,209 are still another type of system which relies upon the interaction of a color precursor and a developer to form images.